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Drug interactions between oral contraceptives and antibiotics
B D Dickinson1, R D Altman, N H Nielsen
1Council on Scientific Affairs, American Medical Association, Chicago, Illinois 60610, USA. barry_dickinson@ama-assn.org
Obstetrics and Gynecology
|November 13, 2001
Summary
Antibiotics can reduce the effectiveness of oral contraceptives (OCs), leading to unintended pregnancies. While most antibiotics show no significant interaction, rifampin is a notable exception, and some individuals may experience reduced OC efficacy with other antibiotics like tetracyclines.
Area of Science:
- Pharmacology
- Reproductive Health
- Drug Interactions
Background:
- Oral contraceptives (OCs) are widely used for pregnancy prevention.
- Potential drug interactions between antibiotics and OCs can compromise contraceptive efficacy.
- Understanding these interactions is crucial for patient counseling and preventing unintended pregnancies.
Purpose of the Study:
- To systematically review and evaluate the scientific evidence regarding drug interactions between antibiotics and oral contraceptives.
- To determine if antibiotic use leads to a significant failure rate of oral contraceptives.
Main Methods:
- Conducted comprehensive literature searches of MEDLINE and Lexis/Nexis databases (1966-1999).
- Included studies reporting on antibiotic therapy and OC efficacy in compliant users, pharmacokinetic effects, or ovulation induction.
- Analyzed case reports, clinical surveys, and pharmacokinetic data.
Main Results:
- Over 30 pregnancies reported in women using both OCs and antibiotics, particularly rifampin.
- Approximately 20% of pregnant women in family planning clinics reported concomitant OC and antibiotic use.
- Most oral antibiotics, except rifampin, did not significantly alter OC pharmacokinetics or ovulation, but individual variations were observed, especially with tetracyclines and penicillins.
Conclusions:
- Rifampin demonstrably impairs the effectiveness of oral contraceptives.
- While systematic pharmacokinetic interactions are uncommon for most antibiotics, individual patients may experience reduced OC efficacy.
- A cautious approach is recommended due to the inability to predict which individuals will experience significant interactions.